In a melt-spinning for a polyester filament yarn, an increase as large as possible in the extruding rate of the polymer through a spinneret significantly contributes to enhancing the productivity of the polyester filament yarn. In the current fiber industry, the above-mentioned increase in the extruding rate is considered to be preferable from a point of view of a cost reduction in the production of the polyester filament yarn.
As a typical means for enhancing the productivity of the polyester filament yarn, a method in which the extruded polyester filament yarn is taken up at an increased speed to increase the extruding rate of the polyester filament yarn through the spinneret is known. In this conventional method, however, since the taking-up speed of the extruded polyester filament yarn is high, and thus the degree of orientation of the polyester molecules in each polyester filament increases, the resultant filament yarn disadvantageously exhibits a decreased residual elongation. Therefore, naturally, the maximum draw ratio of the polyester filament yarn in the subsequent drawing step or draw-false twisting step decreases. Thus, the disadvantageous decrease in the drawing property of the polyester filament yarn in the drawing or draw-false twisting step offsets the extruding rate-increasing effect due to the increase in the taking-up speed.
As one means for solving the above-mentioned problem, European Patent Publication No. 47464-A1 discloses a polyester filament yarn-producing method in which an addition-polymerization product of an unsaturated organic monomer is added as a filament elongation-enhancing agent to a polyester resin, to increase the residual elongation of the resultant melt-spun polyester filament yarn. In this method of the European patent publication at, for example, page 9, line 3, the addition polymerization product finely dispersed in the particle form molecular size in the polyester resin, and the resultant fine particles of the polymer are considered to serve as rollers or runners for the polyester resin. The European patent publication discloses, as a practical example of the addition-polymerization product, "DELPET 80N". In an actual measurement result, the polymer exhibited a thermal deformation temperature of 98.degree. C.
The above-mentioned method of the European patent publication is useful for producing a partially (or pre-) oriented polyester filament yarn (POY) and a melt-spun polyester filament yarn having a high residual elongation, namely an as-spun filament yarn, and a polyester filament yarn (FOY) produced, under a super high speed, by a coupled spinning and drawing process. However, when the inventors of the present invention have an attempt to wind up the as-spun polyester filament yarn as disclosed in the European patent publication and having a high residual elongation by using a commercially-available winder, they were confronted with new problems.
Namely, the inventors of the present invention have found that in practice, the as-spun polyester filament yarn could not be wound up by the conventional winder, and a wound package of the yarn could not be formed. As phenomena relating to this problem, it has been found that since one or more filaments in the yarn exhibited a poor traverse printing property, in the resultant wound package, a cob-webbing phenomenon in which the yarn fell outside of the edges portion, in the form of a normal circumferential winding state of the wound package, and an irregular winding in the edge portion thereof, by which the surface of the edge portion was disberted to result in destruction of the wound package, occurred. Further, a yarn-float on the yarn package during the yarn was being wound, occurred, and this phenomenon caused bursting of the package. Thus these phenomena may cause a fatal blow against the polyester filament yarn.
The causes of the above-mentioned problems are considered to be that, since the addition polymerization product particles are not compatible with the polyester resin and serve as rollers or runners for the polyester resin, these particles superiorly bleed out on the peripheral surface of the polyester filament to cause the peripheral surface to be too rough, and thus a friction of the filaments with each other (F/F friction), and a friction of the filaments with a metal (F/M friction) to decrease. Therefore, the winding performance of the resultant polyester filament yarn decreases or becomes uneven.
To prevent the decrease in the F/F friction and the F/M friction, a person with ordinary skill in the art will expect to provide a means in which an oiling agent for increasing the F/F friction and the F/M friction is applied to the extruded polyester filament yarn and then the oiled yarn is taken-up and wound. Friction-increasing agents include alkyleneoxide-addition product modified with an aromatic ring or a polyhydric alcohol, for example, polyoxyethylene-octylphenyl ether, polyoxyethylene-nonylphenyl ether, polyoxyethylene-noxylphenyl stearate, polyoxyethylene-p-phenyl ether, and polyoxyethylene-benzylphenyl-phenol ether; and glycerolpropyleneoxide (PO)/ethylene oxide (EO) addition products, sorbitol PO/EO addition product and sorbitan PO/EO addition products. Also, friction-increasing agents include low viscosity compounds having a low lubricating property, for example, polypropyleneglycol with a low molecular weight of 500 to 700; rosin esters and silica.
In fact, when the fiction-increasing agent was applied to the extruded polyester filament yarn before winding, a yarn package could be prepared in a good form. However, when the wound polyester filament yarn was withdrawn from the package and subjected to a subsequent processing, for example, drawing or a false-twisting, formation of fluffs and breakage of the yarn frequently occurred, and thus the processing could not continue and a poor yarn was produced. Therefore, the employment of the friction-increasing agent was unsuccessful in essentially solving the above-mentioned problems.
The term "an improved winding performance", used in the present invention refers to a performance of the polyester filament yarn in that the polyester filament yarn can be stably and smoothly wound in a drawing or draw-texturing processing step without using an oiling agent as described above, which causes formation of fluffs or breakage of the yarn.